Most "clone" video games are considered legal, as long as they don't take the actual art/text/music/etc. from the original. Game design is usually very difficult to copyright. Whether or not they're ethical is another story.

You could just ask the original author about it; just because they licensed it as CC doesn't mean they can't also license it to you in a different way, should they want to.

Well...I thought I was done, but, when I try the game in any emulator that isn't FCEUX, it immediately crashes...

Actually, it crashes 10 frames into the title screen... somehow it successfully makes it out of famitone2, at the end of NMI, but as soon as it pla's...rti...the stack address points to address $0000, = BRK, crash.